Various derivatives of 5,6-dihydro-pyrrolo[2,1-a]isoquinoline have a number of valuable pharmacological properties [(C. Casagrande, A. Invernizzi, R. Ferrini, and G. G. Ferrari, J. Med. Chem. 11, 765, 1968; C. Casagrande, A. Invernizzi, R. Ferrini, and G. Miracoli, Farmaco, Ed. Sci. 27, (12), 1029-1044 (1972); S. A. Siphar, (Erf. G. Ferrari and C. Casagrande), Brit. Pat. No. 1,153,670 (5/29/69) (Chem. Abstr. 71, 81215g); N. Nakayama, N. Imamura, T. Kanazawa, and S. Yoneda, Heterocycles 20, (1), 168 (1983)]. In spite of their pharmacological importance, this group of compounds has hitherto been used only to a small extent due to the inadequate methods of synthesis.
In the majority of syntheses known in the literature, the tricycle is closed by reacting tautomerizable 1-alkyl-3,4-dihydroisoquinolines with 1,2-biselectrophiles. [C. Casagrande, A. Invernizzi, R. Ferrini, and G. G. Ferrari, J. Med. Chem. 11, 765, 1968; J. Thesing and H. F. Funk, Chem. Ber. 19, 1546-1551 (1958); Y. Ban and M. Terashima, Chem. Pharm. Bull. 13 (7) 775-785 (1965); S. Sakai, A. Kubo, M. Inaba, M. Katagiri, and K. Tanna, Yakugaku Zasshi 86 (9), 856-858 (1966) (Chem. Abstr. 65, 18558a (1966)); H. Meyer, Liebigs Ann. Chem. 1981, 1534-1544]. Due to the limited choice of suitable reactors, the functionality of the pyrrole substituents, generally alkyl, aryl, and ester functions, can only be varied within narrow limits. Other methods are used in special cases [N. Nakayama, N. Imamura, T. Kanazawa, and S. Yoneda, Heterocycles 20, (1), 168 (1983); Ph. Cauwel and J. Gardent, Tetrahydron Lett. 1972 (27) 2781-2784; F. M. Hershenson, J. Org. Chem. 1975, 40 (6), 740-743; E. Breuer, S. Zbaida, J. Pesso, and I. Ronen-Braunstein, Tetrahedron 1977, 33 (10), 1145-1148; S. Kano, T. Yokumatsu, Y. Yuasa, and S. Shibuya, Heterocycles, 19, (11), 2143-2145 (1982); W. E. McEwen, I. C. Wang Huang, C. P. Cartaya Marin, F. McCarty, E. Marmugi Segnini, Ch. M. Zepp III, and J. J. Lubinkowski, J. Org. Chem. 1982, 47, 3098-3105] are interesting only for their reaction mechanisms [M. Hanaoka, A. Wada, Y. Sakamoto, M. Ichihara, S. Yasuda, and T. Imanishi, Heterocycles 16, (11), 1933-1936 (1981); G. Blasko, G. Dornyei, M. Barczai-Beke, P. Pechy, and C. Szantay, Heterocycles 20, (2), 273-278 (1983)].